In third generation partnership project (3GPP) high speed downlink packet access (HSPDA), control information that is necessary for decoding high speed downlink shared channel (HS-DSCH) is transmitted via a high speed shared control channel (HS-SCCH). Multiple HS-SCCHs may be transmitted to a set of wireless transmit/receive units (WTRUs) associated with a particular cell. The HS-SCCH carries two (2) parts of data: part 1 data and part 2 data. The part 1 data includes channelization code set information, modulation scheme information, etc. The part 2 data includes transport block size information, hybrid automatic repeat request (HARQ) process information, redundancy and constellation version information, WTRU identity (ID), etc. An HS-SCCH frame includes three time slots. The part 1 data is transmitted in the first time slot, and the part 2 data is transmitted in the second and third time slots.
FIG. 1 shows conventional HS-SCCH encoding. For encoding the part 1 data, the channelization code set information Xccs and modulation scheme information Xms are multiplexed to generate a sequence of bits X1. Rate ⅓ convolutional coding is applied to the sequence of bits X1 to generate a sequence of bits Z1. The sequence of bits Z1 is punctured for rate matching to generate a sequence of bits R1. The rate matched bits R1 are masked in a WTRU-specific way using the WTRU ID to produce a sequence of bits S1. Masking in this context means that each bit is conditionally flipped depending on the mask bit value. For the WTRU specific masking, intermediate code word bits are generated by encoding the WTRU ID using the rate ½ convolutional coding.
For encoding the part 2 data, the transport block size information Xtbs, HARQ process information Xhap, redundancy version information Xrv, and new data indicator Xnd are multiplexed to generate a sequence of bits X2. From the sequence of bits X1 and X2, cyclic redundancy check (CRC) bits are calculated. The CRC bits are masked with the WTRU ID, (Xue), and then appended to the sequence of bits X2 to form a sequence of bits Y. Rate ⅓ convolutional coding is applied to the sequence of bits Y to generate a sequence of bits Z2. The sequence of bits Z2 is punctured for rate matching to generate a sequence of bits R2. The sequences of bits S1 and R2 are combined and mapped to the physical channel for transmission.
The performance of the detection of the part 1 data is influenced by the Hamming distance between the masks used for multiple HS-SCCHs. The conventional method produces a set of masks with a minimum distance of eight (8). When these minimum distance codes are used, the HS-SCCH detection performance is not optimal. In addition, with implementation of multiple-input multiple-output (MIMO) for HSDPA, more data need to be carried by the HS-SCCH. Therefore, it is necessary to make more room for transmission of data related to MIMO implementation in the HS-SCCH.